Previously we had an internal only _cogl_material_set_user_program to
redirect legacy usage of cogl_program_use() through CoglMaterial. This
instead makes the API public because until we implement our planned
"snippet" framework we need a stop-gap solution for using shaders in
Cogl.
The plan is to also support ARBfp with the cogl_program/shader API so
this API will also allow clutter-gst to stop using direct OpenGL calls
that conflict with Cogl's state tracking.
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